1. Field of the Invention
The present invention relates to a diffusion plate used in a direct-type backlight module and a method for making the same, particularly to a diffusion plate having a microstructure on the illuminated surface thereof and a method for making the same.
2. Description of the Related Art
FIG. 1 shows a schematic view of a conventional direct-type backlight module. The direct-type backlight module 1 is used in a liquid crystal display and comprises a diffusion plate 10, a plurality of lamps 12, a reflector 14, a diffusion film 16, a brightness enhancement film (BEF) 18 and a plurality of diffusion particles 19.
The diffusion plate 10 is a transparent body doped with the diffusion particles 19 therein or thereon. The refractive index of the diffusion particles 19 is different from that of the body of the diffusion plate 10. The light beams in the diffusion plate 10 are diffused due to the refraction of the diffusion particles 19 so that the lamp mura between the lamps 12 can be reduced. The diffusion plate 10 has a top surface 101 and a bottom surface 102, wherein the bottom surface 102 is an illuminated surface for receiving the incident light beams emitted from the lamps 12 directly and the incident light beams reflected by the reflector 14. The top surface 101 of the diffusion plate 10 is attached with the diffusion film 16 and the brightness enhancement film 18. The brightness enhancement film 18 has a plurality of prisms thereon so as to concentrate the diffused light beams within the desired view angle of the liquid crystal display and raise the luminance in the desired view angle of the backlight module 1.
The shortcoming of the diffusion plate 10 is that it only can diffuse the light beams. If the paths of the light beams need to be changed (e.g., concentrated after diffusion), this necessitates other optical films (e.g., the diffusion film 16, and the brightness enhancement film 18). However, the optical defects easily occur on the optical films due to the environmental affect so that the yield of the backlight module 1 is lowered. Additionally, the optical films are expensive, which raises the cost of the backlight module 1. Further, each optical film only has a single optical function, which limits the optical design, and cannot be adapted for various customized designs.
Consequently, there is an existing need for a novel and improved diffusion plate and the method for making the same to solve the above-mentioned problem.